Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
  • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
  • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
  • H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
  • H01S3/094015—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre with pump light recycling, i.e. with reinjection of the unused pump light back into the fiber, e.g. by reflectors or circulators
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/02—Optical fibres with cladding with or without a coating
  • G02B6/02295—Microstructured optical fibre
  • G02B6/02314—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes
  • G02B6/02342—Plurality of longitudinal structures extending along optical fibre axis, e.g. holes characterised by cladding features, i.e. light confining region
  • G02B6/02366—Single ring of structures, e.g. "air clad"
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/06—Construction or shape of active medium
  • H01S3/063—Waveguide lasers, i.e. whereby the dimensions of the waveguide are of the order of the light wavelength
  • H01S3/067—Fibre lasers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
  • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
  • H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
  • H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
  • H01S3/09415—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/08—Construction or shape of optical resonators or components thereof
  • H01S3/08018—Mode suppression
  • H01S3/0804—Transverse or lateral modes
  • H01S3/08045—Single-mode emission
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
  • H01S3/16—Solid materials
  • H01S3/1601—Solid materials characterised by an active (lasing) ion
  • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
  • H01S3/1618—Solid materials characterised by an active (lasing) ion rare earth ytterbium

Definitions

• the invention relates to an optical fiber laser device delivering a transverse monomode beam of high average power.
• the field of the invention is that of high power fiber lasers emitting in the spectral band 970 nm-985 nm.
• the necessary pump power must be as high as possible and the beam must remain at the diffraction limit (that is to say simultaneously present a high power, and a high brightness).
• This harmonic wavelength in blue, about 488 nm is advantageously used in the fields of biology, surgery or medicine.
• the laser sources at substantially 488 nm are generally gas lasers operating with Argon. These sources sometimes include two lines at wavelengths of 514.5 nm and 488 nm.
• Laser sources with two lines at substantially 514.5 nm and 488 nm are produced in a gaseous medium, because there is no solid-state laser medium emitting directly at these wavelengths.
• these laser sources at substantially 488 nm should preferably have an excellent spatial quality in order to focus the beam on as small a volume as possible.
• These laser diodes are preferably related to transverse single-mode laser diodes (low power) and / or laser diodes of power (multimode).
• the choice of these laser diodes can only be a compromise between power and beam quality, which is an undeniable disadvantage in situations where a high power density is required.
• the transverse monomode laser diodes deliver a power limited to a few hundred milliwatts, while the power laser diodes, emitting several watts, have a highly multimode beam, that is to say of low spatial quality. .
• a solution to increase the power is then to use a laser diode with a funnel structure that provides higher power, but with larger spectral widths of the order of 4 to 5 nm .
• the maximum power that such a laser can deliver is limited to about 10 W.
• laser architectures whose amplifying medium is a material doped with Yb ions used to produce laser sources substantially at 976 nm
• These laser architectures include optical pumping devices emitting the 910nm-940nm band
• Solutions based on materials doped with rare earth ions use either crystals or optical fibers in which the doping ions are incorporated.
• the fiber solution has the advantage of being with a fully fiberized solution and therefore compact, ultrastable and reliable.
• the solution provided by the solid-state doped solid-donor amplifying media at substantially 976 nm makes it possible to carry out an opto-optical conversion between the power supplied by the pump and the power delivered by the laser that can go up to 80%.
• the emission of a solid amplifying medium (crystal or silica) doped with ytterbium ions at substantially the laser wavelength of 977 nm implies strong constraints on the geometry of the amplifier (transverse section and length amplifier medium), pump beam and pumping level.
• the pumping intensity must exceed a limit value, called transparency intensity ( ⁇ 30kW / cm 2 ) for silica doped with ytterbium ions when pumped to substantially 915nm and that it is desired to emit at substantially 977 nm ) necessary to perform the optical amplification.
• the amplifying medium is a crystal doped with ytterbium ions
• the necessary pump intensity is obtained by strongly focusing the pump laser, the useful crystal length being limited by the Rayleigh zone of the pump beam.
• the pump source must be chosen sufficiently bright to ensure transparency over the entire length of the crystal.
• the solution provided by the doped optical fiber lifts this constraint along the Rayleigh length, since the pump beam is guided by the fiber, which makes it possible to obtain high pumping intensities over long fiber lengths.
• this pumping technique requires the use of semiconductor laser diodes (or any other laser source) in the band 910 nm - 940 nm limited by diffraction and therefore low power ( ⁇ 1W).
• Another solution consists in guiding a more powerful multi-mode pump in a concentric guiding sheath with a doped core, called a pumping sheath. The latter, however, must have a limited section to ensure at all points of the fiber the local pump intensity condition greater than the intensity of transparency.
• the lengths of fiber necessary to absorb the pump wave injected are typically several meters, or even tens of meters.
• the laser line of a wavelength in the band 1010 nm - 1100 nm, for which these fibers are usually used has a gain much greater than that of the a line around which it is desired to obtain a laser radiation of substantially 977 nm.
• the study of the influence of this parasite gain and the resulting limitations are given in the publication [J.Nilsson, JDMinelly, R.Paschotta, AC Tropper, and AC Hanna, "Ring doped cladding pumped single-mode. level fiber laser ", Opt. Lett. 23, 355 (1998)].
• the invention aims to remedy the problems related to the technical difficulties encountered in the generation of laser sources of a fundamental wavelength in the infrared at a wavelength of substantially 977 nm at the output of a system laser whose amplifying medium is an optical fiber doped with rare earth ions.
• This laser is compact, low cost, high power.
• the invention proposes to improve the high power fiber laser devices by the use of a doped fiber whose core diameter is greatly increased compared to the standard monomode fiber diameters and which is capable of providing a monomode optical guidance of the laser wave so as to increase the power of the laser beam.
• the subject of the invention is a fiber laser device emitting transverse single-mode radiation controlled at a given wavelength comprising:
• At least one laser diode able to emit a pump wave
• said amplifying optical fiber comprising a core of an included diameter; between 12 ⁇ m and 200 ⁇ m and a pump sheath, the fiber being doped with a rare earth dopant
• said device comprises:
• a resonator able to reinject a laser beam at the given wavelength at the two ends of said section
• said resonator comprising selective intra-cavity wavelength elements adapted to cooperate with the injection means so as to filter on the given wavelength and also to reinject into the fiber the unabsorbed pump wave after a passage in the fiber.
• the cooperation of the selective means with the injection means makes it possible to inflict losses in the spectral band of the parasitic radiation 1010 nm-1100 nm.
• the coupling means comprise two lenses, said lenses being chosen from at least one of the following lenses: microlens, cylindrical, elliptical, hyperbolic lenses, or aspherical capacitors;
• the coupling means refer to a coupler comprising N input multimode fibers that can be soldered directly to the fiber-optic outputs of N pump diodes and an output fiber with or without a guiding core supporting propagation of a mode. substantially identical to that of the amplifying fiber, capable of being directly soldered to the broad-core amplifying fiber.
• the coupling means relate to a wide mode optical fiber whose transverse section is progressively thinned so as to adopt a funnel structure.
• the broad-mode fiber has one end having the same diameter as the fiber delivering the pump wave and the other end having the diameter of the sheath of the amplifying fiber so that said funnel is welded at one end to the fiber delivering the pump beam and at the other end is soldered to the broad mode fiber.
• the selective elements relate to an element chosen from at least one of the following elements: a dichroic mirror, an absorbing or interferometric filter, a curvature of the amplifying fiber, a doping element added in the constitution of the core of the fiber amplifier, an external solid network, a prism, a Bragg grating photoinscribed in the core of the amplifying fiber or a Bragg grating external to the amplifying fiber; ]
• the fiber is a broad modal area fiber or an LMA fiber
• the diameter of the pump sheath is between 50 and 800 ⁇ m; -
• the heart has a diameter greater than 12 ⁇ m
• the fiber is doped with an element chosen from at least one of the following elements: ytterbium ions, germanium, phosphorus, boron or fluorine;
• the fiber is capable of emitting a beam at the diffraction limit at the output of the core
• the fiber is intrinsically polarization-maintaining or maintained in a fixed position
• the broad-mode fiber is a micro-structured silica air fiber
• the fiber is rigid because it is held in a pure silica rod with an external diameter greater than 1 mm ("rod-type fiber” fiber technology) -
• the fiber is flexible.
• the sheath of the fiber is a waveguide, adapted to perform the guiding of the pump wave, formed by a ring of air holes, called air duct, having a numerical aperture greater than 0.5;
• the guidance of the wave at the wavelength of substantially 977 nm is achieved by an array of air holes parallel to the optical axis surrounding the doped core;
• the fiber appatient to the family of micro-structured air-silica fibers.
• the given wavelength is in the infrared
• the amplifying fiber is of a reduced length so that the laser gain of the parasitic radiation in the 1010 nm-1100 nm band remains below 60 dB;
• the laser diode delivers powers of 10 to 1000 W.
• the pump wave is coupled to a multimode fiber having a diameter of between 50 ⁇ m and 800 ⁇ m.
• FIG. 1 illustrates a representation of the device according to one embodiment of the invention
• FIG. 2 represents the section of an optical fiber according to one embodiment of the invention
• FIG. 3A illustrates the absorption and emission spectra of ytterbium ions when they are inserted in a silica matrix, which is the case in an optical fiber;
• FIG. 3B illustrates the energy levels of the ytterbium ions;
• FIG. 4 represents the power of the high power fiber laser at three energy levels as a function of the pump power
• FIG. 5A and 5B represents the output spectrum of the laser, according to one embodiment of the invention.
• the device 1 comprises:
• a resonator including wavelength selective elements 5,13 including wavelength selective elements 5,13.
• the lens 10 having a numerical aperture of 0.5 and a focal length of 8 mm and the dichroic mirror 9 is totally reflective at the pumping wavelength at about 915 nm.
• the means for coupling the pump wave in the sheath of the doped fiber comprise two respective focal length lenses 18 mm and 8 mm 14 and 15. and a transparent dichroic mirror at the pump wavelength and reflecting at the laser wavelength 13.
• the selective optics relate to two dichroic mirrors 11 and 12.
• the optical fiber 6 is a photonic crystal fiber also called in English "rod-type photonic crystal fibers". This fiber is of reduced length which does not exceed 1.23 m.
• Photonic fibers are not, like conventional fibers, entirely made of a transparent solid material such as doped silica; in section, a photonic fiber has a network of air holes.
• holes are parallel to the axis of the fiber, and extend longitudinally along the fiber. Practically, these holes can be obtained by manufacturing the preform by assembling capillary tubes or silica cylinders, respecting the pattern of the holes to be obtained in the fiber. Stretching such a preform provides a fiber with holes corresponding to the capillary tubes.
• This fiber 6 is a constituent element of the device 1 which allows to implement a high power fiber laser at three energy levels.
• This type of fiber laser is more compact, more stable and does not need a cooling mode compared to semiconductor technologies. It also has a better beam quality, the beam quality being imposed by the guiding properties of the fiber, so it has a better resolution for marking applications.
• This optical fiber is doped with a rare earth ion which is in this embodiment mainly ytterbium.
• Ytterbium belongs to the category of rare earth ions or metal ions which are commonly used to make laser sources. Of all the ions that can be used, only these ytterbium ions, which are part of the rare earth ions, have a transition towards 976 nm.
• this ratio is between 5 and 100.
• Figure 3A illustrates the absorption and emission spectra of Yb ions
• FIG. 3A illustrates, in particular, that the absorption cross section of Tytterbium in the glasses is much larger than the emission cross section.
• the transmitting cross sections towards 976 nm and the absorption cross sections around 915 nm are higher or lower.
• an absorption band of about ten nanometers wide at mid-height around 915 nm diode pumping can be envisaged. Nevertheless, this strong emission around 976 nm is accompanied by an equally intense absorption.
• the emission takes place between the lowest sub-level of the F5 / 2 byte and the sub-level
• the material doped with ytterbium ions absorbs any radiation around 976 nm in the absence of pumping.
• the pumping of the material will have to be intense enough to carry out the transparency population inversion at the laser wavelength 976 nm in the doped medium.
• the pumping intensity around 915 nm is sufficient to achieve transparency of the doped medium to 976 nm. This intensity, corresponding to the cancellation of the absorption at the 976 nm laser wavelength in the material, is called the transparency intensity.
• this silica fiber doped with Yb ions makes it possible to confine the pump in the doped medium, and to easily reach the intensity of transparency along the length of this doped medium.
• This fiber thus guarantees a strong interaction of the pump beam with the doping ion, over a great length thanks to the confinement of the light in the pumping sheath of the fiber.
• This ytterbium-doped fiber used for this transition is a transverse monomode fiber having record dimensions (diameter of 80 ⁇ m) for a single-mode fiber.
• Such extreme dimensions of the doped core are made possible by the network of very small air holes (smaller than
• the substantially 977 nm signal propagates in the 80 ⁇ m diameter doped core and the substantially 915 nm pump propagates inside the 200 ⁇ m diameter optical cladding with a large numerical aperture greater than 0.7.
• This sheath is defined by a microstructure filled with air (illustrated in Figure 2, item 18). This microstructure has holes much larger than those defining the core (> 2 ⁇ m) in a pattern that preserves the symmetry of the fiber around its longitudinal axis.
• the dimensions of the holes respectively defining the core and the sheath of the fiber can be adjusted according to the desired guiding characteristics: core diameter, numerical aperture of the sheath or core.
• this fiber has a pump absorption of 10 dB / m at 915 nm.
• the laser diode 2 emits radiation at a wavelength of between 910 and 940 nm.
• the pump laser diode used delivers powers of 10W to 1000W
• the pump beam can be delivered directly in free space, or be coupled to a multimode fiber having diameters of 50 to 800 ⁇ m.
• the light from the pump diode is coupled to a transport fiber and then injected into the amplifying fiber 6 through optical means 4.
• These coupling means 4 comprise in this particular configuration two lenses 14 and 15.
• the optical means 4 are designed to couple the light from the transport fiber into the laser fiber.
• these optical means have a magnification which allows the image of the core of the transport fiber of the pump at the laser diode output to have a dimension substantially equal to or smaller than the diameter of the pump sheath of the laser fiber 6.
• these optical means 4 have a numerical aperture equal to or greater than the product ON, / G where G is the magnification of the optical system 4 and ON 1 is the numerical aperture of the transport fiber.
• the optical means are composed of a pair of two aspherical lenses: a first lens 14 of 18 mm focal length and a second lens of focal length 8 mm.
• the lens 15 of 8mm 15 has a numerical aperture of 0.5.
• these two lenses may be microlenses, cylindrical, elliptical, or hyperbolic, or aspherical condensers.
• the coupling means may be:
• a coupler comprising N multimode input fibers capable of being welded directly to the fibrated outputs of N pump diodes and an output fiber capable of being directly soldered to the broad-core amplifying fiber.
• a broad-mode optical fiber whose cross section is gradually thinned so as to adopt a funnel structure.
• This fiber has one end having the same diameter as the fiber delivering the pump wave and the other end having the diameter of the sheath of the amplifying fiber; [075]
• the two ends of this "funnel" fiber are then soldered respectively at the output of the transport fiber of the diode 2 and at the input of the fiber Amplifier with a big heart doped 6.
• the fiber has a geometry that allows a single-mode propagation in the core 19 and multimode in the pump sheath.
• the ratio between the diameters of the core 19 and the pump sheath is less than 10.
• the transverse monomode fiber has significant dimensions with a diameter of the doped core 19 of 80 microns.
• Such dimensions of the doped core are made possible by the network of very small air holes ( ⁇ 100 nm in diameter) decreasing the average index of the cladding and making it possible to obtain a numerical aperture of the heart of the order of 0.01.
• the substantially 977 nm signal propagates in the 80 ⁇ m diameter doped core 19 and the substantially 915 nm pump propagates inside the 200 ⁇ m diameter optical cladding with a large numerical aperture greater than 0.7.
• This sheath is defined by a microstructure filled with air 18.
• This microstructure 18 has holes much larger than those defining the core (> 2 ⁇ m) in a pattern that preserves the symmetry of the fiber around its longitudinal axis.
• the ratio between the transverse surfaces of the doped core 19 of the fiber 6 and the pump sheath 18 must remain in the range 5-100 and preferably closer to 5.
• the sheath of the fiber 6 may have a sheath diameter 18 guiding the pump between 50 and 400 ⁇ m.
• the amplifying fiber has a monomode propagation of the beam in the heart doped at the wavelength of substantially 977 nm.
• the fiber is inherently polarizing or simply held in a fixed position.
• the core of the fiber may contain in addition to the rare earth doping ions one or more of the following chemical species: Germanium, Phosphorus, Boron, Fluorine.
• the doped core of the fiber 18 has a diameter greater than 12 microns. It is therefore a broad modal area fiber or LMA fiber (Large Mode Area).
• the broad mode fiber can be a micro-structured silica air fiber, rigid or flexible.
• the length of the fiber 6 is chosen so that the pumping intensity at the fiber exit is greater than the transparency intensity at the fiber outlet and the undesirable gain in the 1010 nm-1100 nm band is maintained. less than 6OdB.
• the gain at 1030nm is substantially 50 dB.
• the laser wave is reflected by the mirror 9, totally reflecting at the laser wavelength of substantially 977 nm while the pump wave at substantially 915 nm is not reflected. This residual pump is then incident on a mirror 8 strongly reflecting the pump wavelength of 915 nm in this embodiment.
• the pump wave then makes a second trip in the laser fiber, which increases the pump's absorption, and increases the population inversion, as well as the efficiency of the laser.
• this pump recycling means may be a photo-inscribed Bragg grating in the core of the fiber, or a free-space massive Bragg grating, or a prism, or a grating.
• a dichroic mirror 13 is placed between the two optical means 14 and 15. This dichroic mirror is totally reflective around 977 nm and totally transparent at the pump wavelength.
• a second mirror 11 totally reflecting around 977 nm is placed on the path of the laser beam to form a resonator with the face of the fiber opposite the pump.
• the resonator corresponds to mirrors with high reflectivity (HR) or finite reflectivity at the wavelength of substantially 977 nm.
• the fiber-end reinjection devices may be Bragg gratings photo-inscribed directly into the doped core of the reflective fiber at the wavelength of substantially 977 nm, or undoped fiber sections with Bragg gratings. reflecting the wavelength of substantially 977 nm inscribed in the core, these sections of fibers being welded to the amplifying fiber.
• the reinjection devices at the ends of the fiber may be massive Bragg gratings.
• One or more of the elements constituting the resonator may be wavelength selective, i.e. reflective at the wavelength of substantially 977 nm and very low reflectivity in the band (1010 nm - 1100 nm).
• the set of optical elements 5 comprises the mirror 12 which is totally transparent at the 977 nm laser wavelength and has a reflectivity> 99% in the 1010 nm-1100 nm band, and the cavity background mirror 11 which has a transmission> 99% in the 1010 nm - 1100 nm band.
• this set inflicts sufficient losses in the 1010 nm - 1100 nm band for the laser to oscillate spontaneously around 977 nm.
• the means of exerting a wavelength selection relates to:
• one or more dichroic mirrors able to reflect a signal of a defined wavelength
• a doping element added in the constitution of the core of the absorbing fiber in the 1010 nm-1100 nm band, or
• This device 1 thus makes it possible to generate a power laser at around 976 nm making it possible to easily reach powers of the order of several hundred watts, compared to 10W in the state of the art, with a quality of excellent beam.
• the laser 7 delivered is a transverse single-mode beam 7 around 976 nm which is very powerful.
• the laser threshold is reached at the pump power value of the diode from 18W to 915nm. At the maximum pump power available at 230W, the laser produces power up to 94 W at 977 nm.
• the efficiency slope of the laser between the pump power and the laser power is 48%.
• the quality of the laser beam remains excellent at such power values, and the performance of the device is limited by the available pump power of the diode.
• FIG. 5A represents the output spectrum of the laser measured at full output power from an optical spectrum analyzer with a resolution of 0.07nm.
• the laser oscillates spontaneously over a spectral range of 6 nm centered at 977 nm.
• the parasitic emission at 1030 nm is 35 dB below the maximum laser signal at 977 nm.
• FIG. 5B represents the output spectrum of the laser as well as the amplified spontaneous spectrum of the emission obtained by suppressing the feedback of the mirror 11.
• the doped fiber has a core diameter very greatly increased compared to standard monomode fiber diameters (that is to say having cores of diameter ⁇ 12 .mu.m).
• the diameter of the core is chosen between 12 ⁇ m and
• the invention implements the use of special optical fibers with large modal area (LMA) index jump or micro-structured, may have record heart diameters> up to 80 ⁇ m currently while providing single-mode optical guidance of the laser wave around 977 nm.
• LMA large modal area
• the device according to the invention also makes it possible to obtain a high-power laser at 488 nm since it has an excellent spatial quality making it possible to focus the beam on as small a volume as possible and a power sufficient to obtain efficiencies. important in the nonlinear stage.
• This device constitutes a solid-state laser medium emitting directly at wavelengths at substantially 488 nm, which has the advantage of being less bulky, more reliable and less expensive than devices using a solid medium emitting between 800. and 1100 nm to which is added a non-linear optical stage for performing frequency mixing or doubling.
• These devices implement a method of producing radiation at 976 nm or 1029 nm and doubling it in frequency.
• Such a nonlinear frequency doubling stage imposes strong constraints on the characteristics of the fundamental beam at 976 or 1029 nm.
• the invention is not limited to the embodiments described and illustrated. It is furthermore not limited to these exemplary embodiments and the variants described.
• the photonic optical fiber may be doped with rare earth ions or metal ions other than Ytterbium ions.

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